1. Field of the Invention
The present invention relates to a filter and a pressure control valve including the same, and more particularly to a pressure control valve of an ECPS (Electronically Controllable Power Steering) apparatus for controlling the highest reaction pressure of hydraulic fluid acting on a hydraulic pressure reaction part, wherein the pressure control valve prevents the blockage of a filter area for removing foreign matters from the hydraulic fluid supplied from a supply port, thereby ensuring smooth supply of the hydraulic fluid while minimizing change of pressure at the filter area, and the pressure control valve makes it possible to reduce the number of parts, the number of fabricating steps, and the material costs of such a pressure control valve.
2. Description of the Prior Art
As generally known in the art, an ECPS apparatus is a means for controlling the supply of steering power according to a vehicle speed so as to maintain steering stability at a high vehicle speed, and is employed so as to solve a problem with a conventional hydraulic steering wheel which is supplied with the same level of steering power regardless whether the vehicle speed is high or low, thus becoming excessively light at a high vehicle speed.
FIG. 1 is a schematic view showing a construction of a conventional ECPS apparatus, FIG. 2a is a vertical cross-sectional view showing a side of a flow path switching valve, and a PCV (Pressure Control Valve) of a conventional ECPS apparatus, and FIG. 2b is a perspective view showing a filter of a conventional PCV.
As shown in the drawings, a conventional ECPS apparatus of a vehicle includes a hydraulic pump 103 driven by a vehicle engine (not shown), a flow path switching valve 100 for switching flow paths of hydraulic fluid according to a relative displacement between an input shaft 205 and a pinion shaft 210, an actuating cylinder 105 for supplying steering power through the hydraulic fluid transferred from the flow path switching valve 100, a vehicle speed sensor 107 for sensing the vehicle speed, an electronic control device 109 for receiving electric signals from the vehicle speed sensor 107, and a pressure control valve 150 provided at a side of the flow path switching valve 100 so as to control the supply of hydraulic fluid to the hydraulic pressure reaction part 215 under the control of the electronic control device 109.
In such an ECPS apparatus, when a driver manipulates a steering wheel 113, a steering shaft 115 is rotated, and the input shaft 205 connected to the steering shaft 115 via a universal joint 117 is related while being relatively displaced in relation to the pinion shaft 210, so that hydraulic fluid is selectively supplied to the actuating cylinder 105, whereby steering power is applied to a rack bar 119.
In addition, the conventional pressure control valve 150 includes a hollow valve body 251 having a discharge port 220 and a supply port 225 formed in the peripheral wall thereof, a spool 253 slidably fitted in the valve body 251 and having a flow path 257 communicating with the supply port 225, the flow path 257 being formed in the body of the spool 253 and opened downward, an elastic member 255 provided on the top of the spool 253, a cap 235 provided on the bottom of the spool 253, and a second valve 270 provided below the cap 235.
In some cases, the pressure control valve 150 may not include the above-mentioned second valve 270. In that event, the flow path 257 of the pressure control valve 150 is not connected to the second valve but directly connected to a reaction port 233 of a valve housing 240, and hence to the hydraulic pressure reaction part 215.
The valve body 251 is formed in a hollow cylindrical shape with a constant diameter, and has a supply port 225 and a discharge port 220 formed in its peripheral wall, wherein a filter 250 is provided over the inlet side of the supply port 225 so as to filter foreign matters flowing into the pressure control valve together with the hydraulic fluid, and a blockage prevention groove 263 is formed around the valve body 251, the blockage prevention groove 263 having a predetermined depth recessed from the outer peripheral surface thereof into the inside of the supply port 225.
In addition, because the flow path of the pressure control valve 150 is opened at the bottom side of the spool 253, the hydraulic fluid supplied through the supply port 225 is transferred to the second valve 270 formed below the spool 253. Furthermore, because the hollow cap 235 communicating with the flow path 257 is provided on the bottom of the spool 253, the spool 253 is prevented from being released from the valve body 251.
Here, the second valve 270 includes a second valve body 271 which is hollow and has a reaction port 230 formed in the peripheral wall of the second valve body 271, a second spool 272 slidably fitted in the second valve body 271 and having a second flow path 274 communicating with the reaction port 230, the second flow path 274 being formed in the second spool 272 and opened at the top of the second spool 272, a second elastic member 273 provided on the top of the second spool 272, and a solenoid 275 provided on the bottom of the second spool 272.
In the above-mentioned second valve 270, the hydraulic fluid supplied through the flow path 257 flows through the second flow path 274 and to the reaction port 230, thereby being transferred to the hydraulic pressure reaction part 215, and the solenoid 275 moves the second spool 272 axially upward or downward, depending on the vehicle speed, whereby the second valve 270 serves as a means for adjusting the amount of hydraulic fluid supplied to the hydraulic pressure reaction part 215.
The elastic member 255 is interposed between the top of the spool 253 and the inner top of the valve body 251, thereby exerting elastic force biasing the spool 253 axially downward, wherein when the pressure of the hydraulic pressure is larger than the elastic force, the spool 253 is moved axially upward, and when the pressure of the hydraulic pressure is smaller than the elastic force, the spool 253 is moved axially downward, so that the flow path 257 communicates with the supply port 225 or is blocked from the supply port 225, whereby the flow of the hydraulic fluid can be controlled.
A support 259 is provided on the top of the elastic member 255 of the valve body so as to support the elastic member 255, and a control plug 252 is screwed into the top opening of the valve body 251.
The filter 250 consists of one or more support frames 256 and one or more filter screens 258. Although the blockage prevention groove 263 is provided on the valve body, the supply port 225 may be blocked if foreign matters are accumulated at an area where the filter 250 for removing foreign matters from the hydraulic fluid supplied to the supply port 225 and a supply port 217 of the valve housing are abutted with each other, or the supply port 225 may be directly blocked by the filter frames 265. In addition, because the valve body has the control plug 252 screwed into it, the number of parts and the number of fabricating steps of such a pressure control valve are increased.